1. Field of the Invention
The invention relates to a structure and a method for constructing a triple-gate transistor device, particularly a triple-gate transistor.
2. Description of the Related Art
Multiple-gate transistors have a number of different uses. However, construction of vertical multiple-gate devices has always been somewhat difficult, given alignment problems between the gates used in the device.
FIG. 1 shows a cross-sectional view of a double-gate device formed on a silicon substrate 10 having a top gate 12 and a bottom gate 14 formed in a buried oxide layer 16. Construction of gates 12 and 14 in this stacked type of device leads to alignment problems between the vertically separated top and bottom gates 12 and 14, respectively. In addition, care must be taken to provide ample connectivity for gate 14.
Simplification and self-alignment in semiconductor processing methods is constantly advantageous. Hence a method which provides a simplified method for forming a multiple-gate device would be advantageous.
The invention, roughly described, comprises a self-aligned transistor. The transistor includes a first silicon portion on an isolation layer, the silicon portion having formed therein a source region and a drain region separated by a channel region. The channel region has a first side and a second side and a top portion, and a gate oxide surrounds the channel on said first side, second side and top portion. A first, a second and a third silicon gate regions are positioned in a second silicon portion surrounding the first silicon portion about the first side, second side and top portion and the channel region.
In a further embodiment, the invention comprises a method for manufacturing a transistor device. The method for manufacturing includes the steps of: providing a substrate having a buried oxide region; depositing a first nitride mask layer having a pattern overlying a silicon region; forming a trench in said substrate with a depth to said buried oxide; depositing a conformal oxide in said trench; forming vias in said conformal oxide adjacent to said silicon region and removing a portion of said first nitride mask to expose a portion of said silicon region; depositing polysilicon in said vias and on said portion of said silicon region; and implanting an impurity into exposed portions of polysilicon in said trench and of said silicon-on-insulator substrate underlying said second nitride layer.